The Gibbs paradox, the Landauer principle and the irreversibility associated with tilted observers [CL]

It is well known that, in the context of General Relativity, some spacetimes, when described by a congruence of comoving observers, may consist in a distribution of a perfect (non-dissipative) fluid, whereas the same spacetime as seen by a “tilted”‘ (Lorentz-boosted) congruence of observers, may exhibit the presence of dissipative processes. As we shall see, the appearence of entropy producing processes are related to the tight dependence of entropy on the specific congruence of observers. This fact is well illustrated by the Gibbs paradox. The appearance of such dissipative processes, as required by the Landauer principle, are necessary, in order to erase the different amount of information stored by comoving observers, with respect to tilted ones.

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L. Herrera
Tue, 14 Mar 17

Comments: 10 pages Latex. Invited contribution for the special issue “Advances in Relativistic Statistical Mechanics” published in Entropy

General invertible transformation and physical degrees of freedom [CL]

An invertible field transformation is such that the old field variables correspond one-to-one to the new variables. As such, one may think that two systems that are related by an invertible transformation are physically equivalent. However, if the transformation depends on field derivatives, the equivalence between the two systems is nontrivial due to the appearance of higher derivative terms in the equations of motion. To address this problem, we prove the following theorem on the relation between an invertible transformation and Euler-Lagrange equations: If the field transformation is invertible, then any solution of the original set of Euler-Lagrange equations is mapped to a solution of the new set of Euler-Lagrange equations, and vice versa. We also present applications of the theorem to scalar-tensor theories.

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K. Takahashi, H. Motohashi, T. Suyama, et. al.
Wed, 8 Feb 17

Comments: 14 pages

Light radiation pressure upon an optically orthotropic surface [CL]

In this paper, we discuss the problem of determination of light radiation pressure force upon an anisotropic surface. The anisotropy of optical parameters is considered to have major and minor axes so the model is called as an orthotropic model. We derive the equations for the force components from the emission, absorption, and reflection, utilizing the modified Maxwell specular-diffuse model. The proposed model can be used as a model of flat solar sail with anisotropically-dispersed wrinkles.

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N. Nerovny
Tue, 7 Feb 17

Comments: 12 pages

Nonlinear reflection from the surface of neutron stars and puzzles of radio emission from the pulsar in the Crab nebula [HEAP]

Having no any explanations the radiation of high-frequency components of the pulsar in the Crab Nebula can be a manifestation of instability in the nonlinear reflection from the neutron star surface. Reflected radiation it is the radiation of relativistic positrons flying from the magnetosphere to the star and accelerated by the electric field of the polar gap. The discussed instability it is a stimulated scattering by surface waves, predicted more than forty years ago and still nowhere and by no one had been observed.

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V. Kontorovich
Wed, 11 Jan 17

Comments: 14 pages, 4 figures; The Report on the Conference “XXV Scientific Session of the Council of RAS on the Nonlinear Dynamics-2015”, P.P.Shirshov Institute of Oceanology RAS, Moscow, Russia, 19-20 December 2015; based on publication in LOW TEMPERATURE PHYSICS, 42, #8, 672-678 with author’s corrections

Constraints on Bounded Motion and Mutual Escape for the Full 3-Body Problem [EPA]

When gravitational aggregates are spun to fission they can undergo complex dynamical evolution, including escape and reconfiguration. Previous work has shown that a simple analysis of the full 2-body problem provides physically relevant insights for whether a fissioned system can lead to escape of the components and the creation of asteroid pairs. In this paper we extend the analysis to the full 3-body problem, utilizing recent advances in the understanding of fission mechanics of these systems. Specifically, we find that the full 3-body problem can eject a body with as much as 0.31 of the total system mass, significantly larger than the 0.17 mass limit previously calculated for the full 2-body problem. This paper derives rigorous limits on a fissioned 3-body system with regards to whether fissioned system components can physically escape from each other and what other stable relative equilibria they could settle in. We explore this question with a narrow focus on the Spherical Full Three Body Problem studied in detail earlier.

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D. Scheeres
Thu, 1 Dec 16

Comments: Accepted for publication in Celestial Mechanics and Dynamical Astronomy

Dynamics of wide binary stars: A case study for testing Newtonian dynamics in the low acceleration regime [GA]

Extremely wide binary stars represent ideal systems to probe Newtonian dynamics in the low acceleration regimes (<10e-10 m/s/s) typical of the external regions of galaxies. Here we present a study of 60 alleged wide binary stars with projected separation ranging from 0.004 to 1 pc, probing gravitational accelerations well below the limit were dark matter or modified dynamics theories set in. Radial velocities with accuracy ~100 m/s were obtained for each star, in order to constrain their orbital velocity, that, together with proper motion data, can distinguish bound from unbound systems. It was found that about half of the observed pairs do have velocity in the expected range for bound systems, out to the largest separations probed here. In particular, we identified five pairs with projected separation >0.15 pc that are useful for the proposed test. While it would be premature to draw any conclusion about the validity of Newtonian dynamics at these low accelerations, our main result is that very wide binary stars seem to exist in the harsh environment of the solar neighborhood. This could provide a tool to test Newtonian dynamics versus modified dynamics theories in the low acceleration conditions typical of galaxies. In the near future the GAIA satellite will provide data to increase significantly the number of wide pairs that, with the appropriate follow up spectroscopic observations, will allow the implementation of this experiment with unprecedented accuracy.

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R. Scarpa, R. Ottolina, R. Falomo, et. al.
Tue, 29 Nov 16

Comments: Accepted for publication on International Journal of Modern Physics D

Analytical approximation to the dynamics of a binary stars system with time depending mass variation [CL]

We study the classical dynamics of a binary stars when there is an interchange of mass between them. Assuming that one of the star is more massive than the other, the dynamics of the lighter one is analyzed as a function of its time depending mass variation. Within our approximations and models for mass transference, we obtain a general result which establishes that if the lightest star looses mass, its period increases. If the lightest star win mass, its period decreases.

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G. Lopez and E. Lopez
Tue, 18 Oct 16

Comments: 9 pages, 3 figures